Evaluation And Mechanism Of Pythium Oligandrum GAQ1 In Preventing And Controlling Root-knot Nematode And Pepper Blight Diseases

Plant soil-borne diseases have occurred frequently in recent years,causing serious losses to agricultural production.The disadvantages of using chemical products to control soil-borne diseases are becoming more and more obvious.Therefore,it is important to discover of new biological control agent with better effect on the prevention and control of soil-borne diseases of plants.In this study,the biocontrol agent Pythium oligandrum GAQ1,screened for control of oomyctes previously in our group,was used to evaluate its effect and mechanisms of controlling root knot nematode and pepper blight in this study.The main results are as follows:1.Pythium oligandrum GAQ1 has the capacity to control root knot nematode disease cansused by Meloidogyne incognita and promote the growth of tomato plants: The fermentation broth of P.oligandrum GAQ1 has a significant lethal effect on M.incognita,and the lethality to M.incognita was 84.17% at 24 hours after treatment.GAQ1 fermentation broth can significantly reduce the attraction of root knot nematodes to tomato roots and the nematode infestation.Compared with the control group,the tomato roots treated with GAQ1 fermentation broth inhibited the infestation of nematodes,with a reduction of 78.21% at 24 h post inoculation.Through the greenhouse pot experiment,it was found that the treatment of P.oligandrum GAQ1 could significantly reduce the number of root knots of tomato,which was reduced by57.87% compared with the control group.Compared with the control group,the tomato plant height,plant weight and root weight were increased by 36.42%,27.19%and 48.24%,respectively,after the GAQ1 mycelial bulb treatment.The results indicated that P.oligandrum GAQ1 was a biocontrol strain with safe,non-toxic and efficient control of M.incognita.2.Pythium oligandrum GAQ1 induced resistance of tomato against root knot nematodes: Based on RNA-Seq analysis,it reavealed that the P.oligandrum GAQ1 could induce the resistance of tomato plants.A total of 261,081,044 raw read pairs were obtained.After quality control,253,448,656 clean read pairs were obtained.The KEGG and GO analysis showed thatthe differentially expressed genes were enriched in the following metabolic pathways: ribosome,phenylpropane biosynthesis,plantpathogen interaction,plant MAPK signaling pathway,phenylalanine metabolism and biogenesis of secondary metabolites synthesis,etc.Real-time PCR analysis confirmed the differentially expressed genes between GAQ1 treatment and control.The results showed that these differentially expressed genes and metabolic pathways played an important role in the induction of tomato resistance against M.incognita by P.oligandrum GAQ1.3.Pythium oligandrum GAQ1 controlled pepper blight casued by Phytophthora capsici and had a growth-promoting effect on pepper: A series of complementary experiments were performed to investigate the biocontrol effect and the underlying disease prevention mechanism of the newly isolated strain P.oligandrum GAQ1 against pepper blight caused by P.capsici.The antagonistic effect of GAQ1 on P.capsici,the control effect on pepper blight disease,and the growth promotion effect on pepper were investigated,as well as measurement by q RT-PCR of the expression levels of defense-related genes induced by GAQ1.Trypan blue staining results showed that GAQ1 hyphae could entangle,adsorb and parasitize on the surface and penetrate the body of P.capsici hyphae,causing cell die.Dipping the detached pepper leaves in the fermentation broth of GAQ1 before inoculation with P.capsici reduced the leaf lesions diameter by 30.79% compared with the untreated control.Pot trial assay results showed that after inoculation with GAQ1 mycelium,the disease index of pepper blight was significantly lower than that of the control,and the biocontrol effect was 69.16%.q RT-PCR results revealed that GAQ1 induced the relative expression levels of the plant defense related genes PR1,WRKY40,WRKY53,ACCO and GST.Moreover,GAQ1 could promote pepper growth,whereby pot assay results showed that at the 5th week after GAQ1 treatment,pepper plant height,aboveground weight,and root weight were increased by 10.11%,33.23%,and 24.72%,respectively.Meanwhile,the leaf contents of chlorophyll a,chlorophyll b,and carotenoids were increased by 13.72%,12.13%,and 15.99%,respectively.Taken together,P.oligandrum GAQ1 is a promising biocontrol agent with the capacity to control pepper blight effectively and promote plant growth.4.Transcriptomic analysis of Pythium oligandrum GAQ1 induced pepper resistance against Phytophthora capsici: The molecular mechanism of P.oligandrum GAQ1 antagonizing P.capsici was initially revealed by RNA-Seq.A total of 656,451,846 raw read pairs were gained,and 640686944 clean read pairs were obtained after quality control.The GO and KEGG analysis on the differentially expressed genes found that these genes were enriched in riboflavin metabolism pathway,glyoxylate and dicarboxylic acid metabolism,biosynthesis-related pathways of secondary metabolites,and glycolysis/gluconeogenesis,etc.metabolic pathways.These pathways and their related genes may play an important role in the control of pepper blight by P.oligandrum GAQ1.Further experimentation will be concucted to discover the function of these genes in control of pepper blight disease.